Socket wrenches are extremely valuable tools because such wrenches have interchangeable sockets that mount upon a driving stub of a socket wrench head, and each socket makes a snug sliding fit upon a polygonal head of a rotatable threaded fastener which may be either a bolt or a nut. Such sockets may be used with any of several fastener driving tools which include a socket wrench as above stated, or a pneumatic nut driver, or a screwdriver type hand tool which has a shaft with a socket at the end.
Interchangeable sockets for fastener driving tools have been known for many years, and the principal objection to them is that a different socket is required for each different size of threaded fastener; and that drawback is greatly increased in the United States of America because of the continued use of English unit fasteners concurrently with the adoption of metric unit fasteners. The result is that at the present time a socket wrench set to fit all fasteners from about 1/4" to about 2" requires an inordinate number of sockets.
Certain attempts have been made to provide an adjustable socket, but the only ones known to applicant have numerous parts and are so cumbersome that they cannot be used in many restricted spaces where socket wrenches are required.